1. Field of the Invention
The present invention relates to a semiconductor, heterostructure superlattice structure suitable for use in various kinds of semiconductor devices such as a field effect transistor (FET), a hot electron transistor (HET), a heterojunction type bipolar transistor (HBT) and so on.
2. Description of the Prior Art
To make various kinds of semiconductor devices, such as an FET, an HET, an HBT and the like, operable at high speeds, it is desirable that the electron mobility in such devices be as high as possible. In order to enhance the electron mobility, there is known in the art a method for increasing the purity of a semiconductor layer in an electron active region. According to this method a two-dimensional electron gas layer is used to avoid impurity scattering.
Although it is desirable to enhance the electron mobility even more, and various methods have been proposed to realize this purpose, the electron mobility near or at room temperature is determined in practice by the electron scattering caused by longitudinal optical (LO) phonons within the structure. Therefore, there is a problem that prevents realization of an adequately high electron mobility.